The increasing integration of LSIs has led to finer and finer circuit line widths of semiconductor devices. An approach employed to form desired circuit patterns on semiconductor devices uses a step-and-repeat exposure system to reduce and transfer, onto a wafer, a high-precision master pattern (also called a mask, or a reticle particularly when used in a stepper or scanner) formed on a piece of quartz. The high-precision original pattern is written with an electron beam writing apparatus by use of a so-called electron beam lithography technique.
For example, there are writing apparatuses that use multiple beams. Using multiple beams can significantly improve throughput, because more beams than in the case of writing with a single electron beam can be applied at the same time (i.e., in a single shot). For example, a multi-beam writing apparatus allows an electron beam emitted from an electron gun to pass through a shaping aperture array having a plurality of holes to form multiple beams, each of which is blanking-controlled by a blanking aperture array. Then, beams that have not been blocked are reduced by an optical system and applied to a substrate on a movable stage.
The electron gun and the shaping aperture array are provided with an alignment mechanism therebetween, which includes an alignment coil and an aperture member and adjusts the optical axis of the electron beam. After the optical axis is adjusted by the alignment coil, the electron beam passes through the aperture member and illuminates the shaping aperture array. The shaping aperture array has a plurality of holes arranged in a matrix with a predetermined array pitch. Multiple beams are formed by allowing the electron beam to pass through the plurality of holes of the shaping aperture array. A beam array (multiple beams) applied to the substrate ideally has a pitch that is obtained by multiplying the array pitch of the plurality of holes of the shaping aperture array by a desired reduction ratio.
In the adjustment of the optical axis of the electron beam carried out by the alignment mechanism, it is particularly important to adjust the angle of incidence such that the electron beam is perpendicularly incident on the aperture member. If the angle of incidence is not well adjusted, the beam array applied to the substrate is partially lost. This affects the measurement and evaluation of the beam shape, and interferes with improvement in writing accuracy.